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Power Line Circuits
Last Updated on: Friday, March 12, 2010 12:07 PM

 

Circuits Designed by Dave Johnson, P.E. :
  • ISOLATED AC CURRENT MONITOR
    This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding.  The transformer contains a single turn primary with a low 0.001-ohm resistance.  It can easily handle 30 amps of AC current and provides at least 500vac of isolation.  With the components shown, the output AC voltage is scaled so 1 amp of current produces 100mv of AC voltage.
  • UNPLUGGED POWER CORD ALARM
    Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. The device was designed to snap onto the outside of a power cord, where it senses the AC electric field emitted. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.

 

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

220 Volt Live Wire in Wall Scanner - This circuit senses power lines behind walls (added 9/04)

3˝ Digit DVM IC Measures Power Factor - 04/28/94 EDN-Design Ideas: circuitry in Fig 1 allows  ICL7106/7107) digital-voltmeter IC, IC4, to measure power factor to0.1% resolution and operate from a single 9Vdc supply. An important feature of  circuit is that variations in load current, line voltage,.....(design idea added 09/05)

AN-872: TP3420A Line Interface Circuit Considerations - National Semiconductor Application Note  (app note added 6/06)

Calculating Power Dissipation for Differential Line Drivers - National Semiconductor Application Note  (app note added 2/06)

Off Line Power Supply Requires Few Parts - 02/17/94 EDN-Design Ideas: -This simple non-isolated off-line power supply can provide up to150 mA5V and uses only a handful of components from110-230-Volt AC input voltage. Note that the low voltage output is directly connected to the mains; it cannot be used when the low voltage part can be touched.....(design idea added 3/03)


           
 
 
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